Inkjet printing is a type of computer printing that recreates a digital image by depositing droplets of ink onto a substrate, such as paper or plastic. Many contemporary inkjet printers utilize drop-on-demand (DOD) technology to force droplets of ink from a reservoir through a nozzle onto the substrate. Accordingly, the mounting and positioning of the reservoir and nozzle (among other components) is critical to accurately depositing drops of ink in the desired position. Together, these components form a print head (also referred to as a “print head assembly”).
Inkjet printers must position individual droplets of ink with high accuracy and precision in order to output images of acceptable quality. However, sufficient accuracy and precision are often difficult to achieve using conventional manufacturing techniques, which often result in inconsistent placement of printer components and poor print quality.
There are many possible sources of error that can contribute to inaccurate and/or imprecise droplet positioning. For example, one key contributor is the physical position of each print head with respect to all six degrees of freedom when mounted inside an inkjet printer housing or printing mechanism. Adjustment mechanisms are commonly used to adjust or align the position of a single print head or multiple print heads within an array.
The desired image quality drives the accuracy requirements and/or precision requirements that a given adjustment mechanism must provide. For example, position tolerance requirements are commonly less than 10 microns (μm), though some applications may require significantly less. Conventional adjustment mechanisms include finely threaded screws, incline planes, cams, eccentric pins, differentials screws, etc., that act against an opposing preloaded force, which is typically applied by a spring. Relative motion between different bodies can then be controlled in multiple degrees of freedom by contacting surfaces that slide against one another. Locking devices, such as screws, are typically used to secure the different bodies in the desired arrangement after adjustment.
However, conventional adjustment mechanisms for adjusting the position of print heads are largely unable to address several challenges. For example, because the resulting position of the print head must be measured to great accuracy, the adjustment mechanism must have very fine resolution. Bodies or surfaces that slide against one another are inherently over-constrained due to flatness or form errors that exist along the surfaces. As another example, changes in the final position can be influenced when locking screws are loosened and tightened. Therefore, resolution of any adjustments is limited due to friction of the sliding surfaces as differences in static friction and dynamic friction between the bodies creates hysteresis.
Mechanical components (e.g., screws, cams, and incline planes) that act to push or pull a body relative to another body must have a means to control undesirable motion in other degrees of freedom. Accurate linear or rectilinear motion requires tight-tolerance parts or features and suffers the same drawbacks of friction between opposing parts, features, surfaces, bodies, etc. Opposing preload forces are required to nest the moving body against the adjuster. Such opposing preload forces are typically provided by a spring. Such a configuration requires higher quantities of parts and larger volumes to fit the parts as compared to an inherently preloaded design. Moreover, adjustment mechanisms typically require more physical parts and time to perform the alignment. The level of skill required by an operator or technician to perform an alignment is high due to potential variations in the adjustment process and tool operation details.